An adaptor for a computing device provides the ability to transfer power from a power source to the computing device so that the computing device can operate and/or charge a battery of the computing device. In some examples, the adaptor may output a fixed voltage that corresponds to the voltage requirement of the computing device. In other examples, the output voltage may be negotiated such that the adaptor can provide a range of voltage levels. For example, the adaptor may be a Universal Serial Bus (USB) with power negotiation capabilities such as a USB-PD compliant adaptor.
However, the output voltage provided by the adaptor may be affected by the impedance or resistance associated with the adaptor's cable. The drop in voltage caused by the cable's resistance may be referred to as IR drop. In some conventional approaches, the output voltage may be compensated to account for the voltage drop in order to provide the level of voltage required by the computing device. For example, cable IR drop compensation may be performed on the transformer's primary-side or the transformer's secondary-side. For adaptors having power negotiation capabilities, conventional primary-side cable IR drop compensation may be difficult to achieve. Secondary-side cable IR drop compensation is based on the transformer's secondary output voltage which will increase as current increases. However, conventional designs for secondary-side cable IR drop compensation may be less effective when output voltage is varied and may be subjected to a long delay time for cable IR drop compensation to be effective. Furthermore, conventional designs for secondary-side cable IR drop compensation may be complicated and expensive.